Lead-free halide perovskites have attracted interest in the photovoltaic industry out of concern for the toxic nature of the lead. Antimony-based perovskite, cesium antimony iodide (Cs3Sb2I9), is one such material proposed to substitute the lead-based perovskites, as it has a high absorption coefficient, nearly direct bandgap, and low effective mass. A clear understanding of the stability of this material will bring out its efficient use in photovoltaics. Here we have studied the degradation of both the polymorphs of Cs3Sb2I9 (dimer and layer forms) in water, light, and elevated temperaturethe well-known factors causing degradation in perovskites using X-ray diffraction and thermogravimetric analysis. The layered polymorph is found to be more stable compared to the dimer polymorph. The dimer form completely degrades in ∼49 days and the layer form in ∼88 days, although both polymorphs of Cs3Sb2I9 are relatively more stable than the established organic–inorganic halide perovskites. We found that the diffusion of iodine from the system is the prime reason for the degradation in Cs3Sb2I9. Also, the reactivity of antimony iodide (SbI3) in oxygen adds up to accelerate the degradation process. Light, water, and heat equally cause the degradation of Cs3Sb2I9, and hence, use of this material for application in the ambient atmosphere would need proper encapsulation or necessary measures.
We show that the colloidal growth of SnS nanosheets (NS), a group IV metal chalcogenide (MC), on MoSe2 NS, a transition metal dichalcogenide (TMDC), results in the formation of type-II nanoheterostructures (NHS). The MoSe2/SnS NHS synthesis is accompanied by in situ generation of MoO3–x at the MoSe2 and SnS interface activating the otherwise electrochemically inert basal planes of MoSe2 NS. The MoSe2/SnS NHS exhibit more active sites, and the built-in electric field at the interface enhances the rate of charge transfer. The largely enhanced electrocatalytic activities are attributed to the electronic property manipulation due to the synergistic interactions between MoSe2 NS and SnS NS. This work provides insights into the design of multicomponent low-dimensional 2D/2D (D = dimension) NHS based on TMDC/MC combination with enhanced electrochemical properties, in particular for applications of water splitting.
Anion exchange of CsPbX3 nanocrystals (NCs) is an easy pathway to tune the bandgap over the entire visible region. Even, mixing of pre-synthesized CsPbBr3 and CsPbI3 NCs at room temperature...
Nanoheterostructures (NHSs) based on lead halide perovskites (LHPs) and chalcogenide quantum dots have proved to be promising candidates for photovoltaic device applications. However, understanding the defect chemistry at the interfaces of LHPs and chalcogenides is essential to stabilize them and further tune their optoelectronic properties. Here, we demonstrate a route for designing CsPbBr 3 −PbSe NHSs and other derivatives of LHP-based NHSs using defect-rich MoSe 2 nanosheets (NSs) and study the effect of the size of PbSe NPs on their optical properties. In this synthesis route, PbSe nanoparticles (NPs) are formed at an early stage of the reaction through a unique cation displacement reaction, over which CsPbBr 3 nanocrystals (NCs) are epitaxially grown. Using this methodology, a nearly 3-fold enhancement in photoluminescence (PL) is achieved, whereas other selenium precursors, which form larger PbSe NPs, result in negligible PL enhancement with respect to the pure CsPbBr 3 NCs. Detailed density functional theory (DFT) calculations suggest that the PbSe NPs are responsible for passivating the surface defects that consequently enhance the PL intensity. However, in the case of larger PbSe NPs, the associated valence and conduction bands lie within the band-gap region of CsPbBr 3 , creating a type-I heterostructure between the two materials, thereby affecting the luminescence properties. Strong passivation of surface defects in CsPbBr 3 −PbSe NHSs is also evidenced from low-temperature PL studies. Furthermore, the resulting CsPbBr 3 −PbSe NHSs demonstrate enhanced stability in the presence of water and do not degrade under ambient conditions for several months.
Two-dimensional (2D) layered Ruddlesden−Popper metal halide perovskites (MHPs) show enhanced stability compared to threedimensional (3D) MHPs. The general formula of 2D layered perovskite is L 2 A n−1 M n X 3n+1 , where L is the large organic spacer and n is the number of metal octahedra. However, the syntheses of such 2D layered perovskites yield a mixture of 3D and 2D layered perovskites with different layers of the metal octahedra. In this work, we have synthesized 2D layered (MA) n+1 Pb n I 3n+1 perovskite by the sonochemical method. We have shown that the dimensionality n can be controlled by the sonication time and reaction temperature. Using absorption and photoluminescence spectroscopy, we have probed the reaction and growth mechanisms of the 2D layered perovskites and their transformation to 3D MAPbI 3 (MAPI). At both lower temperature and early stage of the reaction, 2D layered perovskites with lower dimensionality form and eventually covert to higher-dimensional layered perovskite before transforming to 3D perovskites. The dissimilarity in the solubility of the precursors (PbI 2 and MAI) is responsible for such transformations. We show that these mixed (2D layered and 3D MAPI) perovskites can be used to fabricate a white light-emitting diode.
Cu-based ternary chalcogenides have received significant interest as an alternative to conventional photovoltaic materials. CuInS2 or CuInSe2 are the most studied copper-based ternary chalcogenides for photovoltaics. Recently, copper tantalum sulfide...
The health hazards associated with heavy metal ions in water demand the development of efficient and portable sensors, for rapid onsite detection of these ions. Several research groups have developed colorimetric/visual sensors based on plasmonic nanomaterials and quantum dots (QDs). Attempts for specific detection of metal ions have been partially achieved through the interaction between the metal ion and the passivating ligands around the QD. However, the underlying mechanism is not clearly understood. Here, we have used water-soluble Mndoped ZnS QD to effectively detect Hg 2 + , Pb 2 + , and Cd 2 + through the quenching of QD emission and understand the mechanism of sensing. Stern-Volmer plots indicate that the quenching is static in nature for Pb 2 + , and Cd 2 + , while for Hg 2 + , it is a combination of static and dynamic quenching. Overall, the metal ions bind to the QD through the passivating ligand. After excitation, the electron from the conduction band of the QD can get injected to the metal ion -which decreases the photoluminescence of the QD. The electron injection depends on the reduction potential of the metal ion, the orbital overlap and the overall stabilization energy of the metal ions bound to the QD. Hence, this method of sensing is not selective to a specific metal ion. A solid state sensor of QD-rGO composite detects Pb 2 + down to 0.4 ppb. The findings will be important for future improvement of colorimetric/visual sensors based on QD emission.Heavy metal ions such as lead, mercury and cadmium pose severe potential threats to living beings as they can easily be accumulated in the body and cannot be detoxified by any chemical or biological processes. [1][2][3] Detections of these toxic metal ions are important and have received considerable interest. [4][5][6][7][8][9][10][11][12] Instrumental techniques such as inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectroscopy (AAS) are considered ideal methods to detect heavy metal ions at very low concentrations (∼ subppb). However, these methods suffer from disadvantages such as requirement of sophisticated instruments, time consump-tion, and high cost. Detecting heavy metal ions using rapid and easy methods with high sensitivity is a focal point of research.In the last two decades, there has been a significant development of several optical, [4][5][6][7] electrochemical, [8][9][10] and gel based sensors, [11,12] for sensing of heavy metal ions at trace levels (∼ 10 ppb). Sensors based on plasmonic nanomaterials show a change in color (shift in absorption wavelength) upon addition of the toxic heavy metal ions, depending upon the affinity of the heavy metal ion towards the surface capping agent on the nanoparticles. [13][14][15][16] These methods are restricted to solution state sensing and do not exhibit quick response. Therefore, there is an urge to develop visual sensors, which can effectively detect heavy metal ions rapidly (within seconds) under ambient conditions. [17] Due to their tunable and high photolumin...
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